AI Deciphers Mysterious 217-Year-Old Letter from Napoleon

A coded letter written by Napoleon Bonaparte's stepson in 1809 has been deciphered for the first time in over two centuries, thanks to the application of artificial intelligence. The letter, sent by Eugene de Beauharnais, Viceroy of Italy, to General Auguste de Marmont, had remained a mystery because its key was lost.

Carter Church, an engineer at cybersecurity firm SentinelOne, utilized GPT-6 Astra, an AI model developed by OpenAI, to crack the cipher. The process, which involved analyzing the letter's unique symbols, numbers, and stray letters, took approximately six hours to complete. Church shared on X that the AI handled the entire multi-modal workflow from a single image and goal.

The letter, dated March 16, 1809, begins with a standard French greeting: "You must have received, General Marmont, my letters of the 8th, 14th, and 20th of this month." The subsequent 24 lines, however, were encoded, obscuring Napoleon's intended message.

According to the deciphered message, the letter contained crucial military intelligence and directives. It detailed the disposition of French and allied armies, noting the presence of 40,000 Bavarians under the Duke of Danzig, 30,000 Poles with Prince Poniatowski, and 80,000 French troops under the Duke of Auerstaedt. It also mentioned other forces, including 60,000 men under the Duke of Rivoli and an elite corps of 40,000 commanded by General Oudinot.

The message specifically highlighted the movement of Russian forces against Austria and stated that the army of Friuli numbered 80,000 men. It urged Marmont, whose troops were stationed in Dalmatia and potentially isolated by Austrian territory, not to be intimidated by any perceived threats. "When you receive the order to march, you must not allow yourself to be intimidated by a few troops or a gathering of rabble," the letter advised.

Church noted that while the cipher itself was not inherently complex and could have been solved by human cryptographers with sufficient time and effort, the AI's speed and efficiency in transcribing, cataloging, translating, and then cracking the code represent a significant advancement. He suggested that AI is increasingly capable of tackling complex, niche problems that specialists may lack the bandwidth to address.

The Napoleonic Wars, a series of major conflicts pitting the French Empire against various European coalitions, spanned from 1803 to 1815. France, led by Napoleon Bonaparte, sought to establish dominance over Europe. Hostilities continued until Napoleon's final defeat at the Battle of Waterloo in 1815, which concluded 23 years of widespread conflict and ended French attempts at continental domination.